Method of making metal alloy powders



3,535,103 METHOD OF MAKING METAL ALLOY POWDERS Cyrus E. Whitfield, Waverly, Ohio, assignor to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Filed Apr. 10, 1968, Ser. No. 720,391 Int. Cl. B22f 9/00; C23c 11/02 U.S. Cl. 75--.5 8 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention was made in the 'course of, or under, a contract with the United States Atomic Energy Commission.

My invention relates to methods of making metal alloys and particularly to methods of making such alloys in powder form.

Alloys in powder form are useful in powder metallurgical and in flame-spraying processes. The production of alloys in powder form heretofore has required steps of fusing the metal constituents in the desired proportion, breaking up the fused mass, and ball-milling the resulting pieces into powder. There is no assurance in such a process of obtaining a powder having either the desired composition or particle size.

SUMMARY OF THE INVENTION It is accordingly one object of my invention to provide an improved method of making a metal alloy powder.

It is another object to provide a method of making a metal alloy powder wherein the composition can be carefully controlled.

It is still another object to provide a method of making a metal alloy powder having a closely controlled average particle diameter.

Other objects of my invention will be apparent from the following description and the attached claims.

In accordance with my invention I have provided a method of making an alloy powder comprising the steps of (a) providing a powder mixture comprising particles of a substrate metal, a mobile metal, and a halide; (b) heating the resulting mixture to a temperature high enough to form a mobile metal halide; (c) cooling the resulting mixture to a temperature at which at least a portion of the metal values in said mobile metal halide are reduced to the metallic state thereby depositing a film of said mobile metal onto the particles of said substrate metal, and repeating the heating and cooling steps until an alloy of the desired composition is obtained.

My method produces a metal alloy powder having a controlled particle size and a controlled composition. The particle diameter of the product is determined by the initial substrate particle diameter and the ultimate composition is determined by the relative amounts of different metals present and the number of heating cycles.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For convenience in describing my invention the terms 3,535,183 Patented Oct. 20, 1970 mobile metal and substrate metal are used in the specification and in the claims and are descriptive of the functions of the materials used in carrying out my process.

The term mobile metal refers to the constituent which deposits onto and diffuses into another constituent during the formation of the alloy.

The term substrate metal refers to the constituent of the alloy which functions as a base onto which at least one other constituent is deposited, and may be either an element or an alloy. It must have a high enough melting point so that it does not melt at the process temperatures.

The characteristics of other elements comprising the alloy determine whether or not a specific element is a mobile or a substrate metal. An element characterized as a mobile metal in a process of making one alloy can be a substrate metal in a process of making another alloy. One factor governing the ability of elements to function as a mobile or substrate metal is the free energy of formation of the halide, and the following list begins with elements most likely to form mobile metals and ends with those most likely to be substrate metals. Each element will be a substrate with respect to those elements preceding it in the list and will be a mobile metal with respect to elements following it. For example, thorium should deposit and alloy with all elements below it on the list; palladium, however, can only be a substrate.

TABLE I 1. Magnesium 10. Plutonium 19. Cadmium 2. Thorium l1. Manganese 20. Cobalt 3. Zirconium 12. Zinc 21. Copper 4. Hafnium 13. Chromium 22. Silver 5. Aluminum 14. Tin 23. Nickel 6. Beryllium 15. Iron 24. Niobium 7. Boron 16. Silicon 25. Tungsten 8. Carbon 17. Lanthanum 26. Molybdenum 9. Titanium 18. Vanadium 27. Palladium The mechanism involved in the movement and deposition of the mobile metal is believed to depend to some extent on the specific metal under consideration. While I do not wish to be bound by any theory, it is likely that elements having multiple valence states are deposited by a disproportion mechanism, although an oxidationreduction reaction may be involved. For those metal halides which do not exist in multivalent forms an oxidationreduction reaction probably governs the alloying. The following equations are presented to illustrate the disproportionation reaction and the oxidation-reduction reaction using aluminum as an illustrative mobile metal.

Disproportionation Heating: 2HCl =+2Al 2AlCl +H Cooling: 3AlCl AlCl -l-2Al My invention is described in more detail below with respect to a metal capable of forming a halide in more than one valent state as the mobile metal.

The mixture of components comprising a mobile metal, its higher valent halide, and the particles of substrate metal is heated to a temperature at which the higher valent halide reacts with the mobile metal to form a halide in a lower oxidation state. This reaction may be represented by the following general equation in which the mobile metal, represented by M, has oxidation states of 1 and 3:

The resulting mixture is then cooled to a temperature at which the lower valent halide disproportionates into the metal and the higher valent halide in accordance with the formula 3 MX MX 2M In this step the metal formed deposits onto the subin making an alloy of nickel and aluminum since its use introduces no extraneous impurities. This inert powder is preferably present in an amount of 50 to 200 percent by weight of the nickel powder. While the A1 particle size is not critical, in order to easily separate it from the prodstrate and in subsequent c cles diffuses into it. 5

In these subsequent cycies the mobile metal deposited net It should be larger l t mckeil P and prefonto the substrate is unexpectedly non-reactive to the erably average particle dlameter 1S m the: range of 60 higher valent halide to the extent that it is not removed to 2 g t h t d t t t f t from the substrate particles in accordance with the first 1 igg g g um i; e g fi zg a equation above. Consequently, the concentration of mo- 0 i t erellion e f i ,fi e d O bile metal within the substrate metal can be increased to ags: i i g ggg g fi s i ip g gging:

11 on a'nin a lar e r t' n of th mo- 3 2 g 0y 6 t 1 g g p Opor 10 6 range of 1000 to 1010 C. Higher temperatures tend to My invention will be described in more detail with a f igq fi t i g g 1 d t process wherein nickel is the substrate material and alumier S 6p 6 P er niass 1s e O a mum is the mobile m ateri a1 temperature at WhlCh AlCl drsproportionates into AlCl In carrying out my invention, nickel particles are first i alumutum metal Thls l deposlts on the heated in the presence of aluminum particles and AlCl mckel. particles l alloys Wlth the nickel The powdef to a temperature high enough to produce AICL The mass 1n this step 18 cooled to a temperature below 1000 lection of an average particle size for the nickel powder is 20 and prfaferfibly to temperatufe of 990 determined by the desired average particle diameter of the The folegomg hefmng and pl p repeated until alloy powder formed an alloy of the desired composition 1s obtamed. In a typi- The Alcla may be provided as a powder; however, in cal case no more than 20 cycles w1ll be enough to alloy the preferred method of carrying out my invention, it is r i l i g wlt.h mckel' 1 d formed in place during the heating step. In this preferred 6 eatmg, an coo PEI-1 are cntlca method a1 uminu m, preferably in the form of a powder, the length of time for these steps is determined by equlpand NH Cl are mixed with the nickel powder. As the menthmltanons' powder mixture is heated NH Cl breaks down into NH The pytassure Whlch these .reactlons 211:6 came? 9 and HC1 and the Hcl reacts with the aluminum powder 1s not cr1t1cal and is also determmed by equipment llmrtato form AlCl The composition of the final alloy is easily Hons controlled by providing aluminum and nickel powders in Havmg thlls descnled my the fcnowmg a ratio equal to the ratio in the desired alloy and repeatamples are glven to Illustrate n m more detall' ing the heating and cooling cycles until the aluminum is EXAMPLE I consumed A powder mlxture conta1n1n by W6l ht 85 parts nlckel h ll n tabl ve the com osltion and nickela alri ini miiii $1 3558 pre sei t i?) some ty pical alloy powders powder having l average partlclefhameter of 5 Q d d n ith m method 15 parts of aluminum powder having an average particle pro m accor a Ce W y diameter of 5 microns, 130 parts of alpha A1 0 having an TABLE II average particle diameter of 80 microns, and 10 parts by Constituents 40 weight of NH Cl was placed in a ceramic container in a wt. ercent furnace which was evacuated to a pressure of 100 microns N M Ni A1phase produced mercury to remove oxygen and moisture. The temperature was raised to about 1000 C. after WhlCh 1t was cooled to 930 C. and the temperature was cycled from about Zeta( %)cD 1020 C. to 930 C. for 20 cycles. During these steps the pressure built up to about p.s.i.g. as a result of evolution Epsilon-delta. of hydrogen from the reaction between HCl and alumigg: num. The resulting powder was removed from the furnace, Delta. screened to remove A1 0 and washed in distilled water Delta plus 50 to remove traces of chloride. The concentration of NH C1 in the mixture is not criti 1 Thiresulting powder had a comliosigion of g 4 on ase and an avera e artic e iameter 0 mical, and a concentration of from 1 to 3 percent is preg p ferred.

Inasmuch as the temperatures employed are high enough 55 EXAMPLES ILV I to sinter the particles, in order to prevent the particles Other all0Y c made in a an Wlth t g eral from sintering an inert powder must be dispersed thrOughmethod described in Example I. The starting materials, out the powder mixture in an amount equal to at least 50 process conditions, and compositions of alloys are given percent by weight of the nickel powder. A1 0 is preferred as Examples II-V in Table III below.

TABLE III Starting material,

parts by wt. Temperature, 0. Number Alloy Metal Other of composition Example No. powders materials Lower Upper cycles wt.pereent H 240 Ni 10 NH lCl 950 1, 030 14 Ni 00 01' 2.5 NH4I 10 Cr 820 Ni 20 NH4C1 050 1,030 31 84.2 N1 111 Cu 1,500 A120 8.8 A1

96 A1 7.0 Cu

544 Ni 20NH1O1 980 1,030 23 87.5 Ni 1V 56 Al 1,400 A1 0 11.0 A1 10 Nb 0.9 Nb

198 F0 10 NH4C1 980 1,030 6 60.3 Fe V 00 Or 471 A120; 26.2 Cr 30 Ni 12.5 Ni

As can be seen from the data of Table III, alloys having more than two components can easily be made in accordance with my method.

The above examples are given to illustrate, not to limit, my invention.

I claim:

1. A method of making an alloy powder comprising:

(a) providing a powder mixture comprising particles of a substrate metal, a mobile metal, and a halide;

(b) heating the resulting mixture to a temperature high enough to form a mobile metal halide;

(c) cooling the heated mixture to a temperature at which at least a portion of the metal values in said mobile metal halide are reduced to the metallic state thereby depositing a film of said mobile metal onto the particles of said substrate metal;

((1) heating said mixture to diffuse, into said Substrate metal, film deposited thereon in step (c) and to form more of said mobile metal halide; and

(e) repeating steps (c) and (d) until an alloy of the desired composition is obtained.

2. The method of claim 1 wherein mobile metal is capable of forming a higher valent halide and a lower valent halide, in step (b) the mixture is heated to a temperature high enough to form a lower valent halide, and in step (c) the mixture is cooled to a temperature low enough for said lower valent halide to disproportionate into said mobile metal and its higher valent halide.

3. The method of claim 1 wherein said mobile metal is selected from the group consisting of aluminum, chromium, niobium, and copper.

4. The method of claim 1 wherein said substrate metal is nickel.

References Cited UNITED STATES PATENTS 1,711,603 5/1929 Lay 117-100 2,875,090 2/1959 Galmiche 1486.3 2,886,469 5/1959 Fitzer 117130 3,157,532 11/1964 Galmiche 117100 3,185,566 5/1965 Galmiche 117130 3,436,249 4/1969 Lambert et a1. 117l30 3,449,151 6/1969 Flicker 117-130 3,449,115 6/1969 Galmiche et al. 75--.5 3,230,077 1/1966 Hiller '7584.5

L. DEWAYNE RUTLEDGE, Primary Examiner W. W. STALLARD, Assistant Examiner US. Cl. X.R. 

